Along with the development of the society and the economy, changing of the living environment and the living habits of the human being, new diseases keep emerging, the diseases controlled by synthetic drugs reoccur and become more severe. Meanwhile, the abuses of antibiotics cause drug tolerance of pathogenic bacteria, resulting in that normal dosage of drugs is insufficient to exert the antibacterial effects as expected. In addition, malignant tumor has become one of the main causes of death, which severely threatens the health and life of the human being. The spreading of the diseases causes new disasters to the human being. In the aspect of agroforestry, the humans are facing the challenges of the tolerance of the pathogenic bacteria to bactericides and chemical pesticides. Therefore, continuous development of new and effective drugs has drawn great attentions. There are a great deal of microbes in the soil, including bacteria, fungi, actinomycetes, virus, protista, and the like. The molecular diversity of the secondary metabolic products of soil microbes is the resource of the research and development of new drugs and new pesticides.
Symbiotic bacteria of entomogenous nematodes in the soil produce secondary metabolic products having physiological activities, such as antibacterial substances, insecticidal proteins, extracellular enzymes, and the like. One of the common features of symbiotic bacteria is the production of antibiotics, which has a broad commercial prospect as an antibacterial substance for inhibiting the growth of bacteria, fungi and yeasts (Webster et al., 2002).
A great deal of research has indicated that the metabolic products of gram negative bacteria such as species of Enterobacteriaceae Xenorhabdus and Photorhabdus, which are symbiotic with Steinernema and Heterorhabditis nematodes, can not only inhibit the growth of various bacteria and fungi, but also show pesticidal activities and activities for inhibiting the growth of tumor cells. Therefore, it has become interested by scientists from home and abroad to seek physiologically active substances from this type of specifically habitated bacteria (Li, 1997; Park, 2001; LIU Wei Jing, 2004; Furgani, 2008). Currently, new antibacterial substances have been discovered from their metabolic products, such as xenocoumacins, nematophin (Li, 1997, 1998), xenorxides (Li, 1998), benzylineacetone (Ji, 2004), xenorxides and xenematide (Lang, 2008), etc. Xenorxides also showed significant antitumor activities.